Junction varactor with high Q factor and wide tuning range
A PN-junction varactor includes a first ion well of first conductivity type formed on a semiconductor substrate of second conductivity type. A first dummy gate is formed over the first ion well. A first gate dielectric layer is formed between the first dummy gate and the first ion well. A second dummy gate is formed over the first ion well at one side of the first dummy gate. A second gate dielectric layer is formed between the second dummy gate and the first ion well. A first heavily doped region of the second conductivity type is located in the first ion well between the first dummy gate and the second dummy gate. The first heavily doped region of the second conductivity type serving as an anode of the PN-junction varactor. Second heavily doped regions of the first conductivity type located in the first ion well at one side of the first dummy gate that is opposite to the first heavily doped region and at one side of the second dummy gate that is opposite to the first heavily doped region, the second heavily doped regions being electrically connected to each other and serving as a cathode of the PN junction varactor.
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1. Field of the Invention
he present invention relates generally to a varactor, and more particularly, to a PN-junction varactor having improved quality factor (Q factor) and extended tuning range.
2. Description of the Prior Art
A varactor is, essentially, a variable voltage capacitor. The capacitance of a varactor, when within its operating parameters, decreases as a voltage applied to the device increases. Such a device is useful in the design and construction of oscillator circuits now commonly used for, among other things, communications devices. Varactors are typically employed in voltage-controlled oscillators (VCOs) where a frequency of an oscillator is controlled by an applied current or voltage. In such instances, the VCOs are used when a variable frequency is required, or when a signal needs to be synchronized to a reference signal.
Numerous varactors have been developed and are employed in integrated circuit technologies, for example, PN-diodes, Schottky diodes or MOS-diodes as a varactor in bipolar, CMOS and BiCMOS technologies. Among these, two varactor structures are most frequently used: the PN-junction varactor and the MOS varactor. Currently the PN-junction varactor is predominantly used in LC oscillators. Both these structures can be implemented using standard CMOS processes.
Referring to
Referring to
The main drawback of the prior art PN junction varactor as set forth in
It is therefore a primary object of the claimed invention to provide a varactor to improve the electrical performance thereof.
It is another object of the claimed invention to provide a junction varactor having improved quality factor and extended tuning range, and a CMOS-compatible method for fabricating the same.
According to the claimed invention, a PN-junction varactor includes a first N-well formed on a semiconductor substrate; a first gate situated over the first N-well; a first gate dielectric layer provided between the first gate and the first N-well; a second gate situated at one side of the first gate and overlying the first N-well; a second gate dielectric layer provided between the second gate and the first N-well; a P+ doping region located in the first N-well between the first gate and the second gate, and serving as an anode of the PN-junction varactor; a first N+ doping region located at one side of the first gate that is opposite to the P+ doping region within the first N-well; and a second N+ doping region located at one side of the second gate that is opposite to the P+ doping region within the first N-well. The second N+ doping region is electrically coupled to the first N+ doping region for serving as a cathode of the PN-junction varactor. The P+ doping region is encompassed by a second N-well, and wherein the second N-well has a doping concentration that is higher than that of the first N-well.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. Other objects, advantages, and novel features of the claimed invention will become more clearly and readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:
The present invention, which provides novel junction varactors for CMOS and BiCMOS technologies as well as a method for fabricating the same, will now be described in more detail by referring to the drawings that accompany the present application. It is to be understood that the conductivity types, device or circuit layout, or materials used as set forth in the following detailed description and figures are only for illustration purpose. The scope of this invention should be construed as limited only by the metes and bounds of the appended claims.
Referring initially to FIG. 3 and
As best seen in
Reference is now made to the embodiment illustrated in
As shown in
As shown in
Those skilled in the art will readily observe that numerous modifications and alterations of the present invention may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended
Claims
1. A PN-junction varactor, comprising:
- a first N-well formed on a semiconductor substrate;
- a first gate situated over said first N-well;
- a first gate dielectric layer provided between said first gate and said first N-well;
- a second gate situated at one side of said first gate and overlying said first N-well;
- a second gate dielectric layer provided between said second gate and said first N-well;
- a P+ doping region located in said first N-well between said first gate and said second gate, and serving as an anode of said PN-junction varactor, wherein said P30 doping region is encompassed by a second N-well, and wherein said second N-well has a doping concentration that is higher than that of said first N-well;
- a first N+ doping region located at one side of said first gate that is opposite to said P+ doping region within said first N-well; and
- a second N+ doping region located at one side of said second gate that is opposite to said P+ doping region within said first N-well, and said second N+ doping region being electrically coupled to said first N+ doping region for serving as a cathode of said PN-junction varactor.
2. The PN-junction varactor according to claim 1 further comprising a first N type lightly doped drain (NLDD) region merged with said first N+ doing region and wherein said first NLDD region extends to said first gate.
3. The PN-junction varactor according to claim 1 further comprising a second NLDD region merged with said second N+ doing region and wherein said second NLDD region extends to said second gate.
4. The PN-junction varactor according to claim 1 wherein spacers are provided on sidewalls of said first gate and second gate.
5. The PN-junction varactor according to claim 1 wherein a salicide layer is formed on said first gate, said second gate, said first N+ doing region, said second N+ doing region, and said P+ doping region.
6. The PN-junction varactor according to claim 1 wherein, in operation, said first gate and said second gate are grounded.
7. A PN-junction varactor, comprising:
- a first ion well of first conductivity type formed on a semiconductor substrate of second conductivity type;
- a first dummy gate formed over said first ion well;
- a first gate dielectric layer between said first dummy gate and said first ion wel;
- a second dummy gate formed over said first ion well at one side of said first dummy gate;
- a second gate dielectric layer between said second dummy gate and said first ion well;
- a first heavily doped region of said second conductivity type located in said first ion well between said first dummy gate and said second dummy gate, said first heavily doped region of said second conductivity type serving as an anode of said PN-junction varactor, wherein said fit heavily doped region is encompassed by a second ion well of said first conductivity type, and wherein said second ion well has a doping concentration that is higher than that of said first ion well; and
- second heavily doped regions of said first conductivity type located in said first ion well at one side of said first dummy gate that is opposite to said first heavily doped region and at one side of said second dummy gate that is opposite to said first heavily doped region, said second heavily doped regions being electrically connected to each other and serving as a cathode of said PN junction varactor.
8. The PN-junction varactor according to claim 7 wherein said first conductivity type is N type, and said second conductivity type is P type.
9. The PN-junction varactor according to claim 7 wherein, in operation, said first dummy gate and said second dummy gate are grounded.
10. The PN-junction varactor according to claim 7 further comprising a lightly doped drain (LDD) formed in said first ion well, and wherein said LDD is merged with said second heavily doped regions and laterally extends to said first/second dummy gates.
11. The PN-junction varactor according to claim 7 wherein spacers are provided on sidewalls of said first dummy gate and second dummy gate.
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Type: Grant
Filed: Nov 27, 2003
Date of Patent: Apr 19, 2005
Assignee: United Microelectronics Corp. (Hsin-Chu)
Inventors: Jing-Horng Gau (Hsin-Chu Hsien), Anchor Chen (Hsin-Chu)
Primary Examiner: Jerome Jackson
Assistant Examiner: Jesse A. Fenty
Attorney: Winston Hsu
Application Number: 10/707,221